Impact of a Single Point Mutation on the Antimicrobial and Fibrillogenic Properties of Cryptides from Human Apolipoprotein B

Host defense peptides (HDPs) are gaining increasing interest, since they are endowed with multiple activities, are often effective on multidrug resistant bacteria and do not generally lead to the development of resistance phenotypes. Cryptic HDPs have been recently identified in human apolipoprotein B and found to be endowed with a broad-spectrum antimicrobial activity, with anti-biofilm, wound healing and immunomodulatory properties, and with the ability to synergistically act in combination with conventional antibiotics, while being not toxic for eukaryotic cells. Here, a multidisciplinary approach was used, including time killing curves, differential scanning calorimetry, circular dichroism, ThT binding assays, and transmission electron microscopy analyses. The effects of a single point mutation (Pro -> Ala in position 7) on the biological properties of ApoB-derived peptide r(P)ApoB(L)(Pro) have been evaluated. Although the two versions of the peptide share similar antimicrobial and anti-biofilm properties, only r(P)ApoB(L)(Ala) peptide was found to exert bactericidal effects. Interestingly, antimicrobial activity of both peptide versions appears to be dependent from their interaction with specific components of bacterial surfaces, such as LPS or LTA, which induce peptides to form beta-sheet-rich amyloid-like structures. Altogether, obtained data indicate a correlation between ApoB-derived peptides self-assembling state and their antibacterial activity.